Currently, there is a need to deliver electric power to implanted medical devices such as artificial hearts and ventricle assist devices. It is possible to deliver power non-invasively through electromagnetic energy transmitted through the skin. However, problems can arise related to the implanted secondary, which receives power from the external primary. Specifically, the secondary can heat-up and injure the subject due to inadvertent non-optimal coupling, including possibly over-coupling or over-coupling, between the primary and the secondary. Because the secondary is implanted and thus relatively inaccessible, a problem can arise and cause injury before the user or the system is aware of the problem. Prior art systems fail to provide mechanisms for addressing these and other issues that concern transfer of electromagnetic energy to implanted medical devices. These and other deficiencies of the prior art are addressed herein.